The invention is concerned with a lance for the flush gas treatment of non-ferrous molten metal, consisting of a steel tube with a connection for the flush gas.
The flushing of molten steels with inert gases has been practiced successfully for years. The flush gas is predominantly introduced into the pan floor by means of porous stones. Insofar as flushing from above by means of lances is concerned, one uses either a stopper rod perforated at the head or lances with an inserted porous ceramic head. The head is customarily screwed on. The crevices are sealed with fire resistant mortar and the lance tubes enveloped with fire brick. The durability of these lances is not great because of the low stability of the ceramic materials with respect to temperature changes.
As a result of the flushing of molten steels with inert gases, the molten mass is homogenized, impurities are flushed out and an even temperature distribution is attained within the molten mass. The rising gas causes a stirring effect in the molten mass which facilitates the blending in of additives. Beyond this, the flow behavior of the molten mass is generally improved.
The flushing of non-ferrous molten metals, essentially has the purpose of degasing the molten mass, in other words, to lower the hydrogen content and to flush oxide impurities to the surface.
As a result, the density values increase, the elasticity or expansion is improved and the structure becomes more fine-grained. Because of the higher purity obtainable due to the flushing, there results an improved workability in forging, rolling, drawing, as well as more problem-free surface treatment.
The more finely divided the inert flushing gas arrives in the molten mass, the better its effect.
According to the size of the charges to be flushed, various feed systems can be chosen. Ideally, the entire floor surface of the melting vessel should be gas permeable. But this can only seldom be realized for construction and heating technology reasons. For charges of between 50 and 500 kg, gas introduction by means of a lance is best suited.
A lance for the flush gas treatment of molten non-ferrous metals presents a series of requirements which could not, up to now, be fulfilled in their entirety. It must be so lightweight that it can also be handled manually. A sheating of fire bricks, as with lances for flushing molten steels, is therefore out of the question. The lance should have a practically unlimited service life. This requires good mechanical accomplishment and good resistance to sudden changes in temperature, useability for temperatures up to 1300.degree. C. and useability for all liquid media which are in any way corrosive and need to be treated with gas. An extremely fine gas distribution is required therewith, according to which the gas bubble size lies in the .mu.-range.